Flexible alert (FA) is a service for prompting a user group which has a guiding number and one or more member numbers. When the guiding number is dialed, the calling will be connected to each member and all the members receive alert simultaneously. When one member hooks off and answers the phone, a session will be established between the caller and the member, the rest of the calling branches will be released.
FA can be classified into two types, namely, single-user type and multi-user type. In a single-user type FA, when one member is busy, the FA group is busy, while in a multi-user type FA, the FA group is busy only when all the members are busy.
In prior art, whether a FA group is busy or not is determined by the home location register (HLR), the network architecture of which is shown in FIG. 1. As shown in FIG. 1, the user equipments (UE) (101, 107) are user terminals representing the caller or one member of FA. BTS/BSC (102, 106) are base station and base station controller, MSC/VLR (103, 105) are mobile switched center/visited location register, and HLR (104) is a home location register.
FIG. 2 shows a processing flow of the busyness of flexible alert (FA) group with multi-user type in prior art. As shown in FIG. 2, HLR sends route requests to the serving MSC of each member of FA (203/205) when receiving a location request from the calling MSC (202). If the user is idle, the serving MSC returns a temporary location digit number (TLDN) (204). If the user is busy, the serving MSC returns the user is busy (206). Then the HLR returns the TLDN1 of UE1 to the calling MSC because the FA is multi-user type (207). At last, the calling MSC initiates the establishment of a calling to TLDN1 to the serving MSC (208).
Based on demand, FA needs to be implemented in a IP media sub-system (IMS). The network structure of IMS is shown in FIG. 3. The UE (301) represents a user equipment involving a calling, which can be a calling equipment or a called equipment. P-CSCF (302) represents proxy-call session control function, it is the session entrance point where a UE is accessed to the IMS network, and is responsible for forwarding the session between a UE and the network. S-CSCF (303) represents serving-call session control function; it is responsible for handling the session request from a UE and performing the initial filtering rule. AS (304) is an application server and responsible for providing service of a UE, such as processing FA service.
In the prior art IMS standards, the problem existed in realizing FA is that no status information representing user busyness is stored in network, thus it cannot be realized to determine directly that a user is busy. Generally, user busyness is determined by a terminal. When a user receives a new session request, if the user is in another session or processing other services, the user returns information of user busyness to the network. For a multi-user type FA, it is only possible of the network to determine that the FA group is busy when all members return information of user busyness. In addition, it is apparent from above description that the interaction for processing the busyness of a FA group with multi-user type via HLR is extraordinary complex, thus resulting in low efficiency in the process.